This invention is concerned with watercraft in general, and in particular with a thrust coupling to be employed when one watercraft pushes another.
The most frequent way of propelling watercraft which do not have --or cannot use-- their own propulsion system, is by towing them with another craft, such as a tug boat. However, there are circumstances when towing is not practicable or even impossible, and when the tug boat or other watercraft must propel its charges by pushing.
The prior art proposes a variety of thrust couplings which are to be employed for transmitting thrust from the pushing vessel to the pushed vessel. Thus, it is known to provide the bow of the pushing vessel with a beam of wood or the like, or to mount on the beam convex plates which may or may not be provided with a covering of high-friction material. Whatever thrust element is mounted on the bow of the pushing vessel, it presses against the stern of the pushed vessel directly or else extends into a vertical guide track that is provided on the stern. If the vessels are wide enough, two or more transversely spaced elements may be employed, in conjunction with two or more guide tracks, if any.
Particularly the type of arrangement utilizing a vertical guide track in which the thrust element can move vertically, has the advantage that the coupled vessels can perform independent vertical movements, a consideration that is important if the vessels encounter waves of any significance.
However, difficulties have been encountered in the prior art with respect to the construction of the thrust element in such a manner as to avoid jamming of the thrust element during relative vertical movement of the connected vessels while continuing to provide the desired transmission of thrust.
Also, it is frequently required that a conventional harbor tug be capable of being employed as the thrust-exerting vessel, and this tug be capable of changing its horizontal orientation relative to the longitudinal axis of the pushed vessel or vessels, e.g., a string of barges, so that the tug in its entirety acts in effect as a rudder for the pushed vessel or vessels. When such requirements are made, the prior art has generally proposed that the pushing vessel be connectd to the pushed vessel or vessels by an arrangement capable of withstanding thrust as well as tensile forces.